Re: [patch 6/8] mm: memcg: remove unneeded checks from uncharge_page()

[Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>]

On Thu, Nov 24, 2011 at 09:06:19AM +0900, KAMEZAWA Hiroyuki wrote:
> On Wed, 23 Nov 2011 16:42:29 +0100
> Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org> wrote:
> 
> > From: Johannes Weiner <jweiner-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> > 
> > mem_cgroup_uncharge_page() is only called on either freshly allocated
> > pages without page->mapping or on rmapped PageAnon() pages.  There is
> > no need to check for a page->mapping that is not an anon_vma.
> > 
> > Signed-off-by: Johannes Weiner <jweiner-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> 
> For making our assumption clearer to readers of codes,
> VM_BUG_ON(page->mapping && !PageAnon(page)) please.

Yep, delta patch below.

> Anyway,
> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org>

Thanks!

---
From: Johannes Weiner <jweiner-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: mm: memcg: remove unneeded checks from uncharge_page() fix

Document page state assumptions and catch if they are violated in
uncharge_page().

Signed-off-by: Johannes Weiner <jweiner-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
 mm/memcontrol.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 2f1fdc4..872dae1 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2992,6 +2992,7 @@ void mem_cgroup_uncharge_page(struct page *page)
 	/* early check. */
 	if (page_mapped(page))
 		return;
+	VM_BUG_ON(page->mapping && !PageAnon(page));
 	__mem_cgroup_uncharge_common(page, MEM_CGROUP_CHARGE_TYPE_MAPPED);
 }
 
-- 
1.7.6.4

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